Due to present and imminent extreme weather patterns, regulation of hydroelectric reservoirs and flood risk management requires better measurement of river flows. To improve reservoir regulation at our hydroelectric scheme in northern part of Malaysia, a budget river flow measurement system have been installed to estimate flows of rivers that fed four of our hydroelectric reservoirs. The main goal of this measurement system is to estimate water flows into four cascade hydroelectric reservoirs using fore-bay and tail race water levels alone as sensors. With limited number of level sensors installed, mathematical computations have been used to estimate incoming cascade flows. The computation is based on mass balance that volumes of incoming flows should be equal to water stored in the reservoirs over a period plus volumes of water discharge from these hydroelectric plants. The volumes are obtained by integration of flows over selected intervals. However, computation of water volume stored in reservoirs can yield a temporary drift result due to resolution error associated with fore-bay water level measurement that has smallest measured change of O.Olm. These volume computations can causes significant errors as the level variations will be amplified by large surface areas of the reservoirs. Although this measurement system has been able to perform as anticipated, further refinements are needed including to estimate water flow travel times between different reservoir systems. Also, as the lowest level of cascaded hydroelectric stations has limited capacity (due to historical background and construction cost) that spillage is often occur, this proposed system can be used in the future to improve its energy output, in addition to reduce risks of flooding downstream.
Abstract:The main feature of a run-off river hydroelectric system is a small size intake pond that overspills when river flow is more than turbines' intake. As river flow fluctuates, a large proportion of the potential energy is wasted due to the spillages which can occur when turbines are operated manually. Manual operation is often adopted due to unreliability of water level-based controllers at many remote and unmanned run-off river hydropower plants. In order to overcome these issues, this paper proposes a novel method by developing a controller that derives turbine output set points from computed mass flow rate of rivers that feed the hydroelectric system. The computed flow is derived by summation of pond volume difference with numerical integration of both turbine discharge flows and spillages. This approach of estimating river flow allows the use of existing sensors rather than requiring the installation of new ones. All computations, including the numerical integration, have been realized as ladder logics on a programmable logic controller. The implemented controller manages the dynamic changes in the flow rate of the river better than the old point-level based controller, with the aid of a newly installed water level sensor. The computed mass flow rate of the river also allows the controller to straightforwardly determine the number of turbines to be in service with considerations of turbine efficiencies and auxiliary power conservation.
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